This invention relates to file updating methods, and more particularly, to file updating methods for files stored on read-only media.
Software programs and data are frequently distributed on large capacity storage media such as compact disc-read only memories (CD-ROM). These devices are preferably read-only devices to preserve the integrity of the data and program files stored on the device. Such storage devices contain multiple data and executable program files for an application program and typically include a program to install the program and data files on a user""s computer. A common application for distributing a computer program and data files is to provide an interface program and data files for employees that use computers remotely from a central site. For example, a company may equip its sales force with CD-ROMs that contain an interface program that retrieves information from the data files. The retrieved data is used to respond to a customer""s questions on product availability or product specifications.
Having timely information available to an organization""s remote personnel or being able to provide program patches and other improvements to update software distributed to end users is important for customer service and product support. When the data or programs stored on read-only media are frequently updated or modified, the cost of providing the program or data updates on new storage media such as another CD-ROM can be prohibitively expensive.
Accordingly, what is needed is a way to update information stored on read-only media without having to produce new read-only media containing the program or data updates for distribution to a company""s customers or remote personnel.
The above limitations of previously known program and data storage read-only storage devices are overcome by a system and method made in accordance with the principles of the present invention. The method of the present invention includes the steps of generating a basis index table identifying the data content of an original file system, generating a file of modification data blocks that may be used to modify the data content of the original file system, and generating a delta look up table for identifying the data blocks in the original file system and the data blocks in the file of modification data blocks that provide the data content for a new version of the original file system. The delta look up table and the file of modification data blocks may be stored for delivery to a computer on which a copy of the original file system is stored. The delta look up table and the file of modification data blocks are then used by the computer system on which a copy of the original file system is stored to provide the data content for a new version of the original file system in way that appears to provide a single file system containing the new version of the file system. Thus, the method of the present invention may be used to generate data for updating the content of a copy of the original file system without having to generate a copy of every file and data block for the new content of the original file system.
Preferably, the method generates the basis index table by building a basis directory entry meta-data table and a basis index data block table. The basis directory entry meta-data table organizes the meta-data for each entry in a directory enumeration of the original file system by entry name. Preferably, the entry name identifies the entry and its parent. The meta-data stored for each entry is known meta-data such as file attributes. The basis index data block table uniquely identifies each data block found within the original file system. For each unique data block identifier, a source file identifier that identifies the source file for the data block, the offset to the first data unit for the block within the source file, and the length of the data block are stored. These two tables may then be used to generate the files for generating a new version of the file system.
The method of the present invention also includes the steps of generating a delta directory map file to identify the structure of the entries in the new version of the original file system, a delta look up table (LUT) file for identifying the location of the data blocks to generate the files in the new version of the original file system, and a delta modification data block file that contains the new data content for the new version of the original file system. The delta directory map file contains the name for the entries in the new version of the original file system, the modification status for the entries in the new version of the file system, the meta-data for each entry having a modification status of xe2x80x9cmodified,xe2x80x9d xe2x80x9ccontents modifiedxe2x80x9d or xe2x80x9cnew,xe2x80x9d the first look up table record for each file entry, and the number of look up table records used to construct the file in the new version of the original file system. The delta look up table contains at least one LUT record for each file entry having a modification status of xe2x80x9ccontents modifiedxe2x80x9d or xe2x80x9cnew.xe2x80x9d An LUT record identifies the source file containing the data block, the location of the first data unit of the data block in the identified source file, the length of the data block, and the offset of the first data unit of the data block in the file being processed. The source file identifier either identifies a file of the original file system or the modification data block file for the new version. The LUT records for all of the files in the new version of the original file system are stored in an LUT file. The location of the first LUT record for a file is identified by a pointer stored in the meta-data of the delta directory map file for file entries having a modification status of xe2x80x9ccontents modifiedxe2x80x9d or xe2x80x9cnew.xe2x80x9d The directory map file may also be used in the computer having a copy of the original file system to generate information for display or use regarding the structure of the new version of the original file system and its new data content. Structure data includes data that is displayed in response to a directory enumeration command or the like. The delta modification data block file contains the data blocks having new data content for the file entries of the new version of the original file system. As the data blocks for the new data content of the new version of the original file system are stored in the delta modification data block file, a delta index data block table is generated. This table includes a unique identifier for each data block stored in the delta data block modification file that has unique data content, an identifier that indicates the version of the delta data block modification file that is the source file for the block, the offset to the first data unit for the data block and the length of the data block. The delta index data block table is appended to the basis index data block table.
The delta directory map file, the delta modification data block file and the delta look up table may be compressed and stored on storage media or downloaded to a computer having a copy of the original file system. The downloaded delta directory map file, the delta modification data block file and the delta look up table file are used to seamlessly regenerate a new version of the original file system. This regeneration of the new version of the original file system is done in a manner which gives the appearance that the contents of the device on which a copy of the original file system is stored have been modified, even if the device uses read-only media for storage of the original file system. Thus, the system and method of the present invention provide a mechanism for updating the contents of a file system without requiring the production of a complete file system corresponding to the new version of the program and/or data stored in the file system.
Preferably, the method and system of the present invention may be used to generate a representation of a new version of an original file system with reference to the original file system and to the delta modification data block files for previous versions of the original file system. This use of previous versions reduces the amount of data to be stored in the delta directory map file, delta modification data block file, and delta look up table for the latest version of an original file system. In this embodiment of the present invention, the process for generating the files for the new version of the original file system produces delta data block records that identify the source file for a data block as being either a file in the original file system, a delta modification data block file for a previous version of the original file system or the delta modification data block file for the new version of the original file system. The version of the delta modification data block table containing a data block is determined from the delta index data block tables appended to the basis index data block table.
These and other benefits and advantages of the present invention shall become apparent from the detailed description of the invention presented below in conjunction with the figures accompanying the description.